Magnesium base alloys



United tates MAGNESIUM BASE ALLOYS No Drawing. Application May 6, 1955 Serial No. 506,661

3 Claims. (Cl. 140-2100) This invention relates to magnesium base alloys.

It has been proposed in the specification of British Patent No. 532,143 to provide magnesium base alloys containing cerium from 0.1% to 2%, zinc between 1.1% and 12% with or without manganese between 0.3% and 0.8%, aluminium not exceeding 1%, and iron at least 0.05%. These alloys have, however, up to the present time not been developed to the point of commercial utilization, in spite of the fact that they offer excellent mechanical properties. A particular problem involved in this type of alloy is the tendency to grain coarsening with consequent reduction in mechanical properties on carrying out heat treatment. Heat treatment has also been accompanied by the further difficulty of tendency to distortion of the castings with consequent necessity for complicated and expensive jigging. it has been further proposed in the specification of British application No. 693,478 to introduce beryllium into this type of alloy by way of an aluminium-berryllium hardener whereby the alloy may contain up to 3% aluminium. We have however found that the presence of aluminium aggravates the above experienced difiiculties on heat treatment.

According to the present invention, alloys of the type in question are subjected to a solution heat treatment commencing at a temperature of at least 400 C. which temperature is increased slowly up to a temperature of at least 445 C. and not exceeding 465 C., the duration of heat treatment, whilst over 440 C., not exceeding that which will produce appreciable grain growth or distortion, and subsequently subjecting the alloy to precipitation heat treatment.

The temperature may be raised continuously or step by step. For example, an increase in temperature of 5 C. each half hour has been found to be convenient and economical.

It has been found that heat treatment, according to the invention, will result in maximum mechanical properties and can be carried out without grain growth or extensive jigging. The alloy, which is usually in the form of castings, after reaching a temperature of at least 445 C., may be maintained at a more or less constant temperature between 445 C. and 465 C. for a short period. The maximum temperature preferably does not exceed 460 C. The precipitation heat treatment may be effected at a temperature of 130-200 C. for a period of 12-50 hours. Preferably the castings are water-quenched at the conclusion of the solution heat treatment before submitting them to precipitation treatment.

For the purpose of the present invention, the type of alloy concerned has a composition defined Within the following limits:

Zinc 5 to 7%.

Rare earth metals 0.2 to 1%.

Manganese 0.3 to 0.7%.

Aluminium Less than 0.1%, preferably less than 0.03%.

23345100 Patented May 13, 1958 Iron Q. 0.01 to 0.1%. Tellurium From nil up to 0.1%, e. g.

0.02 to 0.05%. Beryllium may also be present if desired, e. g 0.0001 to 0.05%. Magnesium Remainder.

0.1% proof stress "tons per square inch 12.2 Ultimate tensile stress do 18.2 Elongation, percent on 2" 4.5

It is a most surprising result that for this type of alloy maximum properties should be achieved with so short a period of solution heat treatment, of which the majority is at a comparatively low temperature.

The alloy was made by melting together the magnesium, zinc, rare earth metal and manganese, the latter being introduced by means of a magnesium base alloy viz. Elektron AM 503, and stirring, the zinc being in the form of a zinc-iron hardener in accordance with the invention described in the specification of patent application No. 9652/53. The hardener maybe in the form of spelter or zinc dross having a composition of about 95% zinc and 5% iron, with practically no aluminium, silicon or other harmful impurities. The manganese can also be introduced by manganous chloride.

I claim:

1. A process for the heat treatment of magnesium base alloys consisting of the following:

4 Zinc 5 to 7%.

Rare earth metals 0.2 to 1%. Manganese 0.3 to 0.7%. Aluminum From nil to 0.1%. Iron 0.01 to 0.1%.

Tellurium From nil up to 0.1%.

Beryllium From nil to 0.05%. Magnesium Remainder.

wherein the alloy is subjected to a solution heat treatment commencing at a temperature of at least 400 C., which temperature is increased slowly up to a temperature of at least 445 C. and not exceeding 465 C., the duration of heat treatment, Whilst over 440 C., not exceeding that which will produce appreciable grain growth or distortion, and subsequently subjecting the alloy to precipitation heat treatment.

2. A process as claimed in claim 1 wherein the alloy is water quenched after heating to at least 445 C. and before subjecting it to precipitation heat treatment.

3. A process as claimed in claim 1 wherein the temperature is increased 5 each half hour up to at least 445 C., the alloy is then quenched and submitted to a precipitation heat treatment consisting of maintaining the alloy at to 200 C. for 12 to 50 hours.

FOREIGN PATENTS Great Britain Aug. 21, 1936 UNITED STATES PATENT OFFICE QEEEIFICATSE F QREETEGN Patent No. 2,834,700 May 13, 195B James H 1 Fetch.

It is hereby certified that error appears in the above mnnbered patent requiring correction and that the said Letters Patent should read as core rested below In the heading to the printed specification, between lines 10 and 11., insert the following:

-- Claims priority, application Great Britain June 11, 1954 Signed and sealed this 5th day of August 1958.

(SEAL) Attest:

KARL Hg AXLINE RGBERT Q. WWESQN Attesting Gfficer fiississsr sf Pstsms 

1. A PROCESS FOR THE HEAT TREATMENT OF MAGNESIUM BASE ALLOYS CONSISTING OF THE FOLLOWING 